1. Field of the Invention
This invention relates to a scroll compressor.
2. Description of the Prior Art
There is known a scroll compressor having a stationary scroll as shown in FIG. 8. The stationary scroll 1 comprises an end plate 11 and a spiral stationary wrap 12 standing upright on the end plate 11 and forming an integral part thereof. The wrap 12 has a uniform height and a uniform thickness and is shaped to for an involute curve. The compressor also has a swivel scroll as shown in FIG. 9. The swivel scroll 2 comprises a disk-shaped end plate 21 and a spiral swivel wrap 22 standing upright on the end plate 21 and forming an integral part thereof. The wrap 22 has a uniform height and thickness and is shaped to form an involute curve. The stationary and swivel wraps 12 and 22 engage each other in the compressor, as shown in FIGS. 10(a) to 10(d).
FIGS. 10(a) to 10(d) illustrate the compressing action of the compressor. The swivel scroll 2 revolves with respect to the stationary scroll 1 without rotating about itself. Specifically, the swivel wrap 22 revolves clockwise with respect to the stationary wrap 12, as shown by FIGS. 10(a) to 10(d). The closed spaces 3a and 4a which are defined by the stationary and swivel scrolls 1 and 2 as shown in FIG. 10(a), gradually diminish in volume and approach the center of the compressor, as shown at 3b and 4b in FIG. 10(b), at 3c and 4c in FIG. 10(c) and at 3d and 4d in FIG. 10(d), until they communicate with a discharge opening 5 in the end plate 11 of the stationary scroll 1. Thus, a coolant gas which is, for example, drawn into the closed spaces 3a and 4a is gradually compressed, and discharged from the discharge opening 5.
If the swivel scroll 2 revolves from its position as shown in FIG. 10(d), in which the end point Y of the inner involute of the swivel wrap 22 is spaced from the stationary wrap 12, to its position as shown in FIG. 10(a), the point Y contacts the outer surface of the stationary wrap 12 and thereby defines a point of intake cutoff. This contact cuts off the inflow of the coolant gas and defines the closed space 3a. At the same time, the end point X of the inner involute of the stationary wrap 12 contacts the outer surface of the swivel wrap 22, and this contact defines another point of intake cutoff and defines the closed space 4a. The swivel scroll 2 thereafter revolves from one position to another as shown in FIGS. 10(a) to 10(d), and while the stationary and swivel wraps 12 and 22 remain in contact with each other, the points of their contact shift clockwise. As a result, the closed spaces 3 and 4 gradually diminish in volume and approach the center of the compressor, whereby the gas is compressed therein.
FIG. 11 shows the stationary and swivel wraps 12 and 22 immediately prior to the communication of the closed spaces 3 and 4 with the discharge opening 5 during the final stage of gas compression. At the starting point D of its outer involute, the stationary wrap 12 is in contact with the swivel wrap 22 at the starting point C of its inner involute. This contact defines a point of discharge cutoff, and keeps the closed space 3 closed. At the starting point B of its outer involute, likewise, the swivel wrap 22 is in contact with the stationary wrap 12 at the starting point A of its inner involute. This contact defines another point of discharge cutoff, and keeps the closed space 4 closed. After further revolution of the swivel wrap 22, the laps 12 and 22 are disengaged from each other to place the closed spaces 3 and 4 in communication with the discharge opening 5, whereupon the compressed gas starts discharging therethrough.
As is obvious from the foregoing, however, the engagement or contact between the wraps 12 and 22 is discontinuous at the two points of intake cutoff and the two points of discharge cutoff. At the points of intake cutoff, the wraps shift from their open or disengaged position to their closed or engaged position, while the reverse occurs at the points of discharge cutoff. At any such point, the force of contact between the wraps makes a discontinuous and abrupt change which produces a large amount of noise and vibration.